Femoral stem fixation. An engineering interpretation of the long-term outcome of Charnley and Exeter stems.

The excellent long-term results for the first-generation Charnley stem may not apply to later versions with flanges. It seems possible that the early design functioned as a taper-slip system, as accepted in the Exeter prosthesis. Comparison with the requirements for the alternative composite-beam system for the femoral component shows considerable differences that have important implications. These include design, surface finish, cementing technique and the interpretation of radiological signs of loosening. A distinction should be made between the requirements for the successful use of the two different engineering systems.